1. Field of the Invention
The present invention relates to asynchronous machines having a rotor, a stator arranged coaxially with the shaft of the machine, and a winding, for connection to a DC source, by means of which the magnetic flux in the machine can be varied.
2. Prior Art In asynchronous machines of the type mentioned above, the voltage can be altered by altering the speed of rotation of the machine. When however, the machine is used as an alternating current electrical generator it is particularly undesirable for the speed of rotation to change since a change in speed of rotation also involves a change in the frequency of the electrical output of the machine.
It is known to use electronic or electromechanical control arrangements to vary the voltage by way of the speed of rotation of a machine which drives the asynchronous machine. These control arrangements are complicated, however, and thus expensive, and the cost of manufacture of such a machine is therefore high. What is more, experience has shown that machines of this kind are less reliable. In hydraulic machines, for example, the regulation of the speed of rotation with known apparatus takes place too slowly.